I'm kinda iffy on the idea of alt costumes that are whole other characters. I'm fine with keeping Alph and the Koopalings, but I wouldn't want to see more exotic deviations like Chrom for Ike, or Dixie for Diddy, ect. Or for anyone to be demoted from separate character to mere costume.

There is no benefit to keeping classes gender-locked. Fates lifting the restrictions on Fighter/Pegasus Knight/Troubador classes was a highlight, even if they then flubbed it by being lazy with the DLC classes.
I don't mind if they have different names (i.e. Maid/Butler, Cleric/Priest) so long as they're functionally identical.

My most wanted is Kamek. Yoshi's Island is my favorite video game and is the only franchise besides F-Zero to not get a second character since the N64 game. Kamek could have a fun, magic-oriented moveset drawing upon both his main appearances in Yoshi games and some of his more recent roles in Mario games as well, with his classic geometric magic as his standard B move of course.
Having trouble with the Final Smash though. He could call in and supersize an enemy since that's what he's known for, but that feels kinda odd and overdone.

Just a list.
New Donk City: We've gotta have something from SMO. I don't think it needs to be particularly gimmicky; maybe even make it similar to the Fourside stage from Melee.
Bowser's Castle: Based on the classic grey-bricks-and-red-lava look from the original Super Mario Bros., with an assailable rooftop based on the final boss arena from Super Mario World. Of course, the drawbridge and axe to chop it down with would be a stage feature.
Minecart Madness: A super-gimmicky DK stage set upon chains of minecarts as they roll along a rollercoaster-like track, with jumps and lane changes and all that good stuff.
Great Plateau: Probably the best singular locale to represent BOTW. Maybe as another "tour" stage like Skyloft, with the platform going through the open fields, temple ruins, snowcap, and forest. Maybe one stop could have a decayed Guardian as a stage hazard.
Yoshi's one of my favorite series, but I'm not particularly picky. Woolly World was a fun stage prematurely repping a fun game, so if they just brought that back I wouldn't mind. They'll probably go with a cheery environment rather than one of the grimmer locales, which is understandable, but if they didn't, Navel Piranha's Castle could be cool with its sewer-like design and potential boss hazard.
Planet Phaaze: It's a freaky, semi-organic planet with glowy blue tendrils and strange wildlife. Plus we could use another Metroid Prime stage.
Pokemon is tough to predict. Sun and Moon don't have any real stand-out locales besides Ultra Space, which could work, or we could just get another "arena that shifts between four types" like the Stadium stages and Kalos League.
Kirby, Kirby, Kirby. My dream would be to have the sky tower area from Return to Dreamland, complete with its iconic stage theme, but it could just be another Superstar-based stage since that's Sakurai's favorite; perhaps Castle Dedede, though it might be too similar to Boxing Ring.
Saturn Valley: It's been in both EarthBound and MOTHER 3, so it's a good shared locale with some... interesting locals.
Fire Emblem is in a difficult spot. Its stages are often original content rather than based on a specific place. If FE16 isn't out in time, we could see the opera house or plains from Fates, or maybe Castle Rigel from Gaiden/SoV.
Lightning Battle: Basically, take the flight segment from Kid Icarus Uprising's Chapter 14, and put a traveling platform in it similar to Lylat Cruise. Only problem is Phosphora being an Assist Trophy.
Twilight River: As far as Pikmin stages go, this one has the unique addition of, well, rivers. With lilypad platforms that drift along it. Plus it's autumnal, in contrast to the two previous Pikmin stages being vernal.
Mor Ardain: Out of all of Xenoblade 2's locales it's pretty unique, being a weird steampunk rust desert cliffside. With really kickass music.
F-Zero, Animal Crossing, Wii Fit, Punch-Out!!, Duck Hunt, and Game & Watch could probably settle for just reprising old stages instead of getting wholly new ones, thanks to lack of material to draw from. Same with Brawl's Summit stage if Ice Climbers return, I loved feeding people to the fish.

Well, the two most obvious things are to NOT pair your units up, and to make sure they both have healing staves (or Potent Potion).
For less obvious advice, each villager on the map will only be attacked by one type of weapon the entire time; so as an example, if at the start of the map there's two villagers, one being attacked by axes and the other being attacked by swords, that's it; no other weapons will spawn, and the axes will always go after the first villager while the swords will always go after the second.

This is quite interesting still. I don't know the first thing about actually rigging a model, but I eagerly await their porting to Gmod at least.
These are from the 3DS version, not the Switch version, right? I wonder if the latter will be rippable one day.

Since nobody answered this question...
"Escape" is a standard full-size mission. Several enemy keeps are locked and guarded by Gatekeepers, and some allied captains are trapped inside these keeps but you don't know which keeps they are. Opening up the right keep will rescue the ally, opening the wrong one will spring a trap and cause a red-aura'd shadow enemy to spawn. You can figure out which keeps are correct by hunting down enemy captains on the map. Once an allied captain has been rescued, they will attempt to advance to a designated escape zone, during which time they'll be harassed by some enemies including an ambush waiting at the escape zone itself. So you've got to rescue your allies from the keeps and then escort them to the dropoff point, and once you do that the enemy base opens as usual.
"Escort the Villagers" is a small challenge-type mission. There are a few unarmed villagers on the map and they'll be harassed by infinitely-spawning enemies. You've got to keep all of them alive until time runs out, but it's often complicated by there being more villagers than you have playable units (meaning you have to juggle your attention) or the appearance of Rally Captains and lightning-strike Mages far away from the main action (meaning you need to wait for an opportunity to leave the villagers unattended while you handle an external threat). If any villager dies, you lose, so healing staves are recommended.

The order that they're listed on the character selection menu might not necessarily coincide with the order that their voice files are sorted by in the game's code.
Though I do suspect the latter option is more likely regardless.
Either way, between this and the dummied-out dialogue and supports, I think it's safe to assume that Owain, Navarre, Oboro, and Niles were supposed to be playable from the start.

Perhaps he was meant to formally join your team when he appears in Chapter 1, instead of being an NPC. That would put him in the same join chapter as Frederick, at least.
Or, perhaps, he would have been listed below Lissa on the selection screen.

Remember how Frederick's Voice Gallery had that secret "Other 2" Easter Egg at the bottom of it, but no "Other 1" in sight?
Turns out it's in Owain's Voice Gallery. Perhaps, assuming Owain was originally planned to be in the base game before being relegated to DLC, he was listed before Frederick in the code.

Amped thankfully is not locked behind a killcount (in fact, of the new attributes, it seems only Legendary is).
That being said, it costs 12,000 gold to transfer, which is a bit pricier than most, but no big deal.

Yeah, I'm already noticing the POWAH.
Do we know just how Owain's skill works yet, by the way? Obviously sticking it on Celica and Cordelia, but I'm wondering what its exact effect is and if it's worthwhile on slightly-less-symmetrical ones.